Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 774.4	$ 1,015.9	$ 1,084.2
Other comprehensive income (loss), net of tax	(5.0)	64.4	(75.4)
Ending balance	804.7	774.4	1,015.9
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(31.3)	(96.4)	(20.8)
Reclassification from AOCI, Current Period, Tax	1.7	41.8	3.2
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	2.9	68.9	5.6
Defined Benefit Plan, Foreign Currency Exchange Rate Gain (Loss)	0.1	0.0	0.0
Other comprehensive income (loss), net of tax	(5.8)	65.1	(75.6)
Ending balance	(37.1)	(31.3)	(96.4)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI, before Reclassifications, before Tax, Attributable to Parent	(5.7)	(12.9)	(39.0)
Other Comprehensive Income (Loss) before Reclassifications, Tax	(2.1)	(4.9)	(14.5)
OCI, before Reclassifications, Net of Tax, Attributable to Parent	(3.6)	(8.0)	(24.5)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent	0.5	1.1	(1.8)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI, before Reclassifications, before Tax, Attributable to Parent	(8.3)	6.8	(90.5)
Other Comprehensive Income (Loss) before Reclassifications, Tax	(3.1)	2.6	(33.8)
OCI, before Reclassifications, Net of Tax, Attributable to Parent	(5.2)	4.2	(56.7)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent	4.1	3.0	10.6
Accumulated Defined Benefit Plans Adjustment, Removal Of Obligation Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent	0.0	106.6	0.0
Accumulated Net Investment Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(0.1)	0.2	0.4
OCI, before Reclassifications, before Tax, Attributable to Parent	1.9	(0.1)	(0.2)
Other Comprehensive Income (Loss) before Reclassifications, Tax	0.7	0.0	(0.1)
OCI, before Reclassifications, Net of Tax, Attributable to Parent	1.2	(0.1)	(0.1)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent	(0.5)	(0.4)	(0.1)
Reclassification from AOCI, Current Period, Tax	(0.2)	(0.2)	0.0
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	(0.3)	(0.2)	(0.1)
Other comprehensive income (loss), net of tax	0.9	(0.3)	(0.2)
Ending balance	0.8	(0.1)	0.2
Accumulated Foreign Currency Adjustment Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(0.1)	0.1	(0.3)
OCI, before Reclassifications, before Tax, Attributable to Parent	(0.1)	(0.2)	0.4
Other Comprehensive Income (Loss) before Reclassifications, Tax	0.0	0.0	0.0
OCI, before Reclassifications, Net of Tax, Attributable to Parent	(0.1)	(0.2)	0.4
Ending balance	(0.2)	(0.1)	0.1
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(31.7)	(96.1)	(20.7)
Other comprehensive income (loss), net of tax	(5.0)	64.4	(75.4)
Ending balance	(36.7)	(31.7)	(96.1)
Foreign Exchange Contract | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(0.2)	0.0	0.0
OCI, before Reclassifications, before Tax, Attributable to Parent	0.0	(0.3)	0.0
Other Comprehensive Income (Loss) before Reclassifications, Tax	0.0	(0.1)	0.0
OCI, before Reclassifications, Net of Tax, Attributable to Parent	0.0	(0.2)	0.0
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent	0.1	0.0	0.0
Reclassification from AOCI, Current Period, Tax	0.0	0.0	0.0
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	0.1	0.0	0.0
Other comprehensive income (loss), net of tax	0.1	(0.2)	0.0
Ending balance	(0.1)	(0.2)	0.0
Alloy Metal Hedge | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0.0	0.0	0.0
OCI, before Reclassifications, before Tax, Attributable to Parent	(0.1)	0.0	0.0
Other Comprehensive Income (Loss) before Reclassifications, Tax	0.0	0.0	0.0
OCI, before Reclassifications, Net of Tax, Attributable to Parent	(0.1)	0.0	0.0
Ending balance	$ (0.1)	$ 0.0	$ 0.0